Atomic force microscope

ABSTRACT

A surface shape of a member to be measured is measured by reflecting measuring light at a reflection surface of a probe and utilizing an atomic force exerting between the probe and utilizing an atomic force exerting between the probe and the member to be measured. In addition to a first scanner for driving the probe, a second scanner for moving a focus position of an optical system is provided. Position conversion data representing a correlation between amounts of control of the first scanner and the second scanner are obtained in advance. By synchronously driving the first scanner and the second scanner, the focus position of the optical system is caused to follow the probe to improve measurement accuracy.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an atomic force microscope capable ofmeasuring a minute shape on the order of subnanometers by using anoptical lever for detecting displacement of a probe.

A probe used in an atomic force microscope includes a flat springportion having an end provided with a sharp pointed portion. On the flatspring portion, a reflection surface is formed. The probe is also called“cantilever” but is herein inclusively described as “probe”.

FIG. 26 shows a constitution of a conventional atomic force microscopedescribed in U.S. Pat. No. 5,560,244. The atomic force microscopeeffects measurement of a member 113 to be measured. A probe 114 isattached to a mount 120, and the mount 120 is attached to a lower end ofa tube scanner 112 movable in X, Y and Z directions. A beam from a lightsource 110 is once focused by a lens 160 to form a point source 162 oflight and is then focused onto a back surface of the probe 114 by a lens163 fixed to the scanner 112. A position of reflected light is detectedby a light detection means 116.

In this constitution, when the probe 114 is brought near to the member113 (to be measured), the probe 114 is bent by a force exertedtherebetween, i.e., atomic force. When the probe 114 is bent, adirection of the reflected light is changed, so that a signal of thelight detection means 116 is changed. Accordingly, by detecting theposition of the reflected light from the probe 114, atomic force exertedbetween the probe 114 and the member 113 can be measured. Such atechnique that displacement at the position of the reflected light isread in an enlarged state has been widely known as an “optical lever”and employed also in the atomic force microscope.

Further, in the atomic force microscope described in U.S. Pat. No.5,560,244, the probe 114 is subjected to scanning along a surface of themember 113 by the tube scanner 112. In this case, a position of the tubescanner 112 on the probe 114 side is moved by the scanning with a fixedposition thereof on the light source 110 side. Accordingly, a positionof the light source 110 is not moved but the lens 163 is moved togetherwith the scanner 112, so that a focus position of the focused light ischanged. In other words, by using an optical system such as a lens orthe like fixed to the scanner, it is possible to always focus light foroptical lever onto the back surface of the probe while permitting thefollowing of movement of the scanner by the light.

FIG. 27 shows a constitution of another conventional atomic forcemicroscope described in Japanese Laid-Open Patent Application (JP-A) No.Hei 5-312561. The atomic force microscope effects measurement of amember 203 to be measured. A probe 209 is provided at an end of a tubescanner 204. At the end of the tube scanner 204, a light source LD isalso fixedly provided. Light emitted from the light source LD is focusedonto a back surface of the probe 209. Reflected light from the backsurface of the probe 209 is caused to enter the light detection means211 through fixed lenses L1 and L2 to detect a position of the reflectedlight. In this embodiment, the position of the reflected light incidentinto the light detection means 211 is enlarged by an optical systemincluding the lenses L1 and L2.

In this constitution, similarly as in U.S. Pat. No. 5,560,244, aso-called “optical lever” principle such that bending of the probe 209is converted into a direction of reflected light. The probe 209 is movedalong a surface of the member 203 by the scanner 204 but the lightsource LD attached to the end of the scanner 204 is moved together withthe probe 209. For this reason, the light is always focused onto theback surface of the probe 209. In other words, by disposing the lightsource at the end of the scanner, the atomic force microscope isconstituted so that the light for optical lever follows movement of thescanner and is always incident onto the back surface of the probe.

Two modes have been known as a measurement mode of the atomic forcemicroscope. One mode is called “DC mode” in which bending of the probeis changed by a force exerting between the member to be measured and theprobe and is thus detected. Another mode is called “AC mode” in whichthe probe is subjected to steady-state vibration at a high frequency anda resultant vibration state of the probe is changed by a force exertedbetween the member to be measured and the probe, thus being detected. Ineither mode, accuracy of movement varies depending on whether or notbending (displacement) of the probe can be measured with accuracy.

Further, in the conventional atomic force microscopes, a technique, forimproving the measurement accuracy, which is called “null-balancemethod” has been used. In this method, instead of measuring a change inposition of reflected light from a probe by a light detection means, theprobe is moved so as not to change the position of reflected light. Amovable axis (shaft) capable of controlling a distance between the probeand a member to be measured is provided and controlled so that bendingof the probe caused by interaction of the probe with the member is keptat a constant level, and an amount of movement of the movable axis istaken as a measured value. By employing such a constitution, even whenthe interaction between the probe and the member has a non-linearcharacteristic with respect to a relative distance between the probe andthe member, it is possible to eliminate an influence of the non-linearcharacteristic.

However, the above described conventional atomic force microscopes havebeen accompanied with the following problems.

(1) Patent deviation between a probe and focus of an optical system iscaused to occur during scanning.

In an atomic force microscope utilizing “optical lever”, a shape of amember to be measured is measured by a position of reflected light fromthe probe. For this reason, it is impossible to effect high-accuracymeasurement unless the focus of “optical lever” is accurately formed onthe probe.

However, in U.S. Pat. No. 5,560,244 and JP-A Hei 5-312561, the tubescanner is used, so that the end of the tube scanner is moved arcuatelywith a fixed position as a center when the probe is subjected toscanning. For this reason, an attitude of each of lenses constitutingthe optical system attached to the scanner is also changed largely. As aresult, a focus position of the optical system is deviated from areflection surface of the probe, so that measurement accuracy isreduced.

Further, in the atomic force microscope, the position of the probe ischanged in an optical axis direction during the measurement. In U.S.Pat. No. 5,560,244 and JP-A Hei 5-312561, when an amount of the changein that case is equal to or less than depth of focus, it is possible tomeasure the position of the probe with high accuracy.

The depth of focus is ordinarily approximately 30 μm in the case ofemploying an optical device having NA=0.1, so that it is possible tomeasure high-accuracy measurement in the case where the member to bemeasured has an unevenness of 10 μm or below. However, in the case of anuneven shape having an unevenness of several tens of microns or above,reflected light is diffused. As a result, it is difficult to effectmeasurement at high accuracy.

Further, light from a fixed light source passes through differentportions of each of lenses constituting an optical system by anoperation of a scanner. However, an actual lens varies in characteristicsuch as refractive index depending on a portion of the lens, so that afocus position is deviated from a designed value when a portion throughwhich light passes is changed. More specifically, during the operationof the scanner, the light-passing portion of each of the lensesconstituting the optical system is changed, so that position deviationof focus of the optical system is caused to occur. As a result, thefocus position and a probe position are deviated from each other.

(2) It is difficult to detect a focus position.

As described above, in the atomic force microscope utilizing the“optical lever”, it is important that a position of the probe is set toa focus position of the optical system. In order to realize thissetting, it is necessary to accurately measure the probe position andthe optical system focus position. However, in U.S. Pat. No. 5,560,244and JP-A Hei 5-312561, these positions cannot be measured. It is alsopossible to consider that both of the focus position and the probeposition are externally observed by an optical microscope and alignedwith each other. However, this is very complicated, thus being lesspractical.

(3) It is difficult to adjust a focus position with lapse of time.

In order to effect high-accuracy measurement, focus is required to bealways formed accurately on the probe as a target of the “opticallever”. As described above, the position of the probe as the target ofthe “optical lever” is moved by the operation of the scanner, so that itis necessary to cause the focus position of the “optical lever” tofollow the probe position in accordance with a motion of the scanning.In U.S. Pat. No. 5,560,244 and JP-A Hei 5-312561, this problem has beensolved by attaching a lens to the scanner or attaching a light source tothe scanner.

However, an apparatus such as the scanner causes a change with lapse oftime due to deterioration of parts etc., so that an amount of the changeis not negligible. In order to meet the motion change of the scanner inview of the change with time, it is necessary to adjust a position andattitude of the lens or the light source attached to the end of thescanner. In U.S. Pat. No. 5,560,244 and JP-A Hei 5-312561, the lightsource and the probe are fixed to the scanner having the optical system,so that it is not easy to effect the adjustment. It is possible toadjust positions of these elements (members) which have been originallyfixed and then fix the elements again. However, this adjustment is verycomplicated, so that complicated adjustment performed frequently is alarge problem from a practical viewpoint.

(4) Alignment adjustment during replacement of a probe is complicated.

An end of the probe is deteriorated due to wearing or the like, so thatthe probe is a consumable part. When the probe is replaced, a positionof the probe is always deviated due to a production error or a mountingerror. For this reason, the optical system is required to be readjustedso that the focus is always formed accurately on the probe as the targetof the “optical lever”. However, in U.S. Pat. No. 5,560,244 and JP-A Hei5-312561, it is difficult to detect the focus position and adjustment ofthe focus position is complicated, so that alignment adjustment duringreplacement of the probe is also complicated. From a practicalviewpoint, complicated adjustment performed frequently is largedeficiency.

(5) It is difficult to meet a multi-probe.

In a conventional technique, it is difficult to develop multi-probingcapable of simultaneously measure many points using a large number ofprobes close to each other with a spacing of, e.g., about 100 μm. When anumber of “optical lever” optical systems in accordance with JP-A Hei5-312561 are disclosed, many light sources lenses, and light detectionmeans are to be disposed close to each other. However, it is impossibleto dispose all these constitutional elements (members) close to eachother. This is because each of the constitutional elements is larger insize than 100 μm. Particularly, the lenses require some aperture ratiofor focusing light, so that it is difficult to reduce the size of thelenses. Further, also in U.S. Pat. No. 5,560,244, a number of lightsources and light detection means are similarly disposed close to eachother, the light sources are provided to the end of the scanning, sothat it is further difficult to reduce the size of the end of thescanning.

(6) It is difficult to effect high-accuracy measurement since the end ofthe scanner cannot be reduced in size.

In U.S. Pat. No. 5,560,244, a light source is provided at the end of thescanner, so that there is a possibility of heat generation at thescanner end. The atomic force microscope is ordinarily directed tomeasurement at high accuracy on the order of subnanometers, so that itis largely affected by a change in temperature. In the conventionalatomic force microscope including a heat generation source disposed inthe neighborhood of a point of measurement, the high-accuracymeasurement cannot be expected. Further, it is necessary to attach thelight source and an optical element for focusing light emitted from thelight source onto the probe at the end of the scanner, so that a weightof the end of the scanner cannot be decreased. When the end of thescanner is heavy, an error during scanning is also large. Thus, thehigh-accuracy measurement cannot be also expected.

SUMMARY OF THE INVENTION

The present invention has accomplished in view of the above describedproblems.

A principal object of the present invention is to provide an atomicforce microscope capable of measuring a shape at high accuracy bycausing a focus position of an optical system to follow a position of aprobe.

According to an aspect of the present invention, there is provided anatomic force microscope for measuring a surface shape of a member to bemeasured, comprising:

a light source for emitting measuring light;

a probe having a reflection surface;

an optical system for focusing the measuring light from the light sourceon the reflection surface of the probe;

a housing for holding the optical system;

a probe scanner, mounted to the housing, for holding the probe andmoving the probe in X direction, Y direction, or Z direction relative tothe housing;

light detection means for detecting the measuring light reflected by thereflection surface;

processing means for processing displacement of said probe in Zdirection on the basis of an output of said light detection means;

focus position movement means for moving a focus position of saidoptical system by shifting an optical path of the measuring light beforethe measuring light enters the optical system; and

control means for controlling drive of the probe scanner and the focusposition movement means,

wherein the control means drives the focus position movement means insynchronism with drive of the probe scanner so that a focus position ofthe measuring light focused by the optical system is on the reflectionsurface of the probe.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view for illustrating Embodiment 1.

FIGS. 2( a) and 2(b) are schematic views for illustrating an action of asecond scanner of an apparatus used in Embodiment 1.

FIG. 3 is a plan view showing a constitution of a first scanner of theapparatus used in Embodiment 1.

FIG. 4 is a perspective view showing the second scanner of the apparatusused in Embodiment 1.

FIG. 5 is a block diagram for illustrating a constitution of a scannercontrol apparatus of the apparatus used in Embodiment 1.

FIG. 6 is a schematic view for illustrating a probe of the apparatusused in Embodiment 1.

FIG. 7 is a schematic view for illustrating a focus of an optical systemand a reflection surface of the probe in the apparatus used inEmbodiment 1.

FIG. 8 is a schematic view showing a map of light amount for obtainingposition conversion data of the apparatus used in Embodiment 1.

FIG. 9 is a flow chart for illustrating steps for obtaining the positionconversion data of the apparatus used in Embodiment 1.

FIG. 10 is a flow chart for illustrating a measuring operation of theapparatus used in Embodiment 1.

FIG. 11 is a schematic view for illustrating Embodiment 2.

FIG. 12 is a schematic view for illustrating an auto focus apparatus ofan apparatus used in Embodiment 2.

FIG. 13 is a schematic view for illustrating an action of autofocusingof the apparatus used in Embodiment 2.

FIGS. 14, 15, 16 and 17 are schematic views for illustrating Embodiments3, 4, 5 and 6, respectively.

FIG. 18 is a perspective view showing a probe assembly of an apparatusused in Embodiment 6.

FIG. 19 is a schematic view for illustrating a relationship between afocus of an optical system and the probe assembly in the apparatus usedin Embodiment 6.

FIG. 20 is a block diagram showing a constitution of a scanner controlapparatus of the apparatus used.

FIG. 21 shows time charts in multi-probing by the apparatus used inEmbodiment 6.

FIG. 22 is a flow chart showing steps for obtaining position conversiondata of the apparatus used in Embodiment 6.

FIG. 23 is a flow chart showing a measuring operation of the apparatusused in Embodiment 6.

FIGS. 24 and 25 are schematic views for illustrating Embodiments 7 and8, respectively.

FIGS. 26 and 27 are schematic views each for illustrating a conventionalembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothe drawings.

As shown in FIG. 1, a member 1 to be measured is held on an XY coarsemovement (adjustment) stage 2 and a first scanner 10 as a probe scanneris provided to a housing 6 fixed to a Z coarse movement stage 5. Aposition of a probe 22 having a reflection surface is finely moved in X,Y and Z directions by the first scanner 10 to bend the probe 22 by aforce acting between the probe 22 and the member 1 to be measured, sothat an amount of movement (displacement) of the reflection surface ofthe probe is measured.

An optical system for measurement is a focusing optical system forfocusing measuring light from a light source 23 on the reflectionsurface of the probe 22 and includes a second scanner 26 as a focusposition movement means for moving the focus position and a lightdetection means 37 for receiving (detecting) light reflected by theprobe 22. In this embodiment, measurement values representing a surfaceshape of the member 1 to be measured are calculated by using outputsignals, i.e., a light position signal and light amount signal of thereflected light, by the light detection means utilizing “optical lever”and X, Y and Z positions of the first scanner 10.

The first scanner 10 and the second scanner 26 are synchronouslycontrolled by a scanner control apparatus (control means) 48. In anatomic force microscope utilizing “optical lever”, it is important thatthe focus position is kept on the reflection surface of the probe 22 inorder to ensure measurement accuracy, so that the focus position isrequired to be moved together with the first scanner 10 since the probe22 is moved by drying the first scanner 10.

FIG. 2( a) is a schematic view showing an optical path from the lightsource 23 for “optical lever” to the probe 22 via the optical systemincluding a lens 33. The measuring light from the light source 23 isrequired to be focused on the probe 22 but the probe 22 is moved in,e.g., X direction. In this case, the focus position is required to bealways located on the probe 22, so that the focus position is moved bymoving the light source 23 in X direction by the second scanner 26. Inthis manner, the first and second scanners 10 and 26 are movedsynchronously, so that the focus is always formed on the probe 22.Incidentally, in the embodiment shown in FIG. 2( a), a similar effect isalso achieved by moving the lens 33 in place of the light source 23.Further, depending on design convenience, it is also possible to deflectan optical axis by disposing a deflection mirror between the lightsource 23 and the probe 22. A similar effect is also achieved by usingan optical system using a plurality of lenses in order to reduce lensaberration.

Further, as shown in FIG. 2( b), in place of the constitution shown inFIG. 2( a), it is also possible to employ such a constitution that adistance between the light source 23 and the lens 33 is fixed. In thiscase, when the probe 22 is moved in X direction by the first scanner 10,the light source 23 and the lens 33 are moved in X direction by thesecond scanner 26. As a result, the focus position is moved, so that itis possible to always form a focus on the probe 22.

Further, the second scanner 26 is also movable in Z direction as anoptical axis direction in addition to the two (X and Y) directionsperpendicular to the optical axis. In the constitution shown in FIG. 2(a), the probe 22 is moved in X, Y and Z directions by the first scanner10. In this case, the focus position is required that it is alwayslocated on the probe 22, so that the light source 23 is moved in X, Yand Z directions by the second scanner 26. Here, a positionalrelationship between the light source 23 and the probe 22 via the lens33 is a conjugation relationship and is configured to form the focus ona back scanner of the probe 22. Further, by synchronizing motions of thefirst scanner 10 and the second scanner 26 to keep amounts of movementof these scanners at a ratio of L1:L2, it is possible to always form thefocus on the probe 22.

In the constitution shown in FIG. 2( b), the measuring light from thelight source 23 is required to form the focus on the probe 22 but theprobe 22 is moved in X, Y and Z directions. In this case, it isnecessary to always form the focus on the probe 22, so that the lightsource 23 and the optical system 33 are moved in X, Y and Z directionsby the second scanner 26. By synchronously moving the first scanner 10and the second scanner 26, it is possible to always form the focus onthe probe 22.

As described above, by providing the second scanner 26 movable in theoptical axis direction in addition to two (X and Y) directionsperpendicular to the optical axis, the focus position and the probeposition are independently controllable three dimensionally.

Further, in this embodiment, the first and second scanners arecontrolled synchronously. More specifically, a focus position of theoptical system and a following error for the probe 22 are obtained inadvance so that a position of the probe 22 moved by the first scanner 10is always the focus position of the optical system, thus preparingposition conversion data. The position conversion data may be preparedby preparing an output map of the light detection means 37 by performingscanning with the second scanner 26 while fixing the first scanner 10and repetitively performing a step of calculating a position of thereflection surface of the probe 22 from the output map in an entiremeasuring area by changing the position of the first scanner 10. It isalso possible to employ such a method that a step of preparing a similaroutput map by performing scanning with the first scanner 10 while fixingthe second scanner 26 is repetitively performed by changing the positiveof the second scanner 26.

According to this embodiment, it is possible to control the focusposition in correspondence with the probe position. Further, it ispossible to meet various motions by such a simple method that theposition conversion data is changed. For example, when the probe isreplaced or when a correction is made with respect to a change with timecaused by deterioration of parts or the like, position conversion datadepending on a probe used may be prepared.

In this embodiment, by providing the second scanner 26 for moving thefocus position separately from the first scanner 10 for moving the probe22, it is possible to control the focus position independently andsynchronously with respect to the probe position by the first scanner10. As a result, it is possible to adjust the focus of the opticalsystem in a three-dimensional manner, so that it is possible to meetdeviation in the optical axis direction and improve measurementaccuracy. Further, it is possible to measure even a member to bemeasured having an uneven shape with an unevenness of several tens ofmicrons while causing the focus to follow the Z axis.

Further, when the following error between the focus position and theprobe 22 is known in advance, it is possible to move the second scanner26 so as to cancel the following error. As a result, it is possible tocause the focus position to follow the probe 22 with accuracy, so thathigh-accuracy measurement can be effected compared with a conventionalmethod. In this case, it is necessary to know the following error inadvance but a method therefor can be employed as described later.Further, in this embodiment, compared with the constitution in which theprobe and the light source are provided to the same scanner, it ispossible to reduce a size of the end of the scanner, thus resulting inreduction in size in addition to the high-accuracy measurement.

Further, also in this embodiment, similarly as in the cases of U.S. Pat.No. 5,560,244 and JP-A Hei 5-312561, the optical axis of “optical lever”is moved by scanning with the probe 22, so that a light beam passesthrough different portions of the lens 33.

However, according to this embodiment, it is possible to independentlycontrol the focus position and the probe position, so that it ispossible to correct lens aberration. As a result, the focus position isnot deviated.

Embodiment 1

FIG. 1 shows an atomic force microscope according to Embodiment 1. Abase 3 is disposed on a vibration isolation stand 4 and on the base 3,an XY coarse movement stage 2 is disposed. On the XY coarse movementstage 2, a member 1 to be measured is set. To a Z coarse movement stage5 provided vertically to the base 3, a housing 6 is provided. Thehousing 6 holds an XY scanner 7 movable in X and Y directions.

FIG. 3 is a schematic view of the XY scanner 7 as seen from above (Zdirection). A main assembly of the XY scanner 7 has a hinge mechanismcut from a metal material and is provided with four X plate springportions 8 formed by wire cut processing, so that an X movement portion9 is movably guided in X direction. In the X movement portion 9, an XYmovement portion 10 a is provided and guided by four Y plate springportions 11. By this constitution, the XY movement portion 10 a ismovably guided in X and Y directions. At a center of the XY movementportion 10 a, a through hole 12 is provided.

With respect to drive in X direction, an X piezoelectric element 13 isprovided and a plunger 14 is disposed opposite to the piezoelectricelement 13. The plunger 14 is a device for pressing something at acertain force by the action of spring. By a force generated by theplunger 14, the X movement portion 9 is pressed against thepiezoelectric element 13. This pressing force is important. Thepiezoelectric element is an element expanding and contracting dependingon a voltage but is susceptible to tensile stress, so that it isrequired to be used in such a state that a compressive force is alwaysexerted thereon.

Similarly, also with respect to drive in Y direction, a Y piezoelectricelement 15 is provided between the X movement portion 9 and the XYmovement portion 10 and a plunger 16 is provided opposite to the Ypiezoelectric element 15. By a force generated by the plunger 16, the XYmovement portion 10 a is pressed against the Y piezoelectric element 15.

By controlling voltages to be applied to the X piezoelectric element 13and the Y piezoelectric element 15, it is possible to control X and Ypositions of the XY movement portion 10 a. At four corner portions in aperipheral area of the XY scanner 7, mounting holes are provided.

In the through hole 12 of the XY scanner 7, as shown in FIG. 1, acylindrical Z fine movement axis (shaft) 18 is disposed movably in Zdirection. The Z fine movement axis 18 is formed of a cylindricalpiezoelectric element provided with electrodes at inner and outerperipheral surfaces thereof and expands and contracts in Z direction byapplying a voltage to both of the electrodes. In this embodiment, afirst scanner 10 movable in three-axis directions (X, Y and Zdirections) is constituted by the XY scanner 7 and the Z fine movementaxis 18. The first scanner 10 is connected to and controlled by ascanner control apparatus 48. The scanner control apparatus 48 is, e.g.,a computer which is called a digital signal processor capable ofeffecting high-speed operation (processing).

At an end of the Z fine movement axis 18, a mounting block 19 isprovided. To the mounting block 19, a vibration imparting piezoelectricactuator 20 and a probe 22 via a probe holder 21 are fixed. The probe 22is inclined with respect to Z direction as shown in FIG. 3. This isbecause the probe 22 is disposed in a direction inclined with respect tothe member 1 to be measured so as to alleviate abutment of a portionother than the tip of the probe against the member 1. This is importantin the case of measuring a recessed surface of the member to bemeasured.

Further, when the vibration imparting piezoelectric actuator 20 isconnected to an unshown oscillation circuit to cause vibration, it ispossible to constitute the above described AC mode atomic forcemicroscope. More specifically, it is possible to measure a force exertedbetween the probe and the member to be measured while vibrating theprobe at high frequency. On the other hand, when the vibration impartingpiezoelectric actuator 20 is omitted, it is possible to constitute theDC mode atomic force microscope. More specifically, it is possible todirectly measure a static force exerted between the probe and the memberto be measured without vibrating the probe.

In either of the AC measurement mode and the DC measurement mode, apoint affecting measurement accuracy is that whether or not bending ofthe probe can be detected with accuracy. Hereinafter, for convenience ofexplanation, description will be continued on the precondition that themeasurement mode is the DC measurement mode.

A light source 23 such as semiconductor laser is fixedly provided to thehousing 6 and light emitted from the light source 23 is guided into anoptical fiber 24. As the light source 23, it is possible to use asemiconductor laser part of a pigtail type. The optical fiber 24 isconnected to an optical fiber emission end 25. When a single modeoptical fiber is employed as the optical fiber 24, light is emitted froma very narrow area having a diameter of several microns, so that such anoptical fiber emission end can be used as a good point source of light.The optical fiber emission end 25, i.e., the point source of light isfixed at an end portion of a second scanner 26 as a tube scanner fixedlyprovided to the housing 6.

FIG. 4 shows a constitution of the second scanner 26. The second scanner26 is a cylindrical piezoelectric element provided with a plurality ofelectrodes. At an inner portion of the piezoelectric element, a commonelectrode 27 is provided. At an outer upper portion, Z directionelectrode 28 is provided, and at an outer lower portion, four-pieceelectrode 29 is provided. For convenience of explanation, a potential ofthe common electrode 27 is taken as zero volts.

In such a constitution, by controlling a voltage between the commonelectrode 27 and the Z direction electrode 28, the piezoelectric elementexpands and contracts in Z direction indicated by an arrow 32. Whenvoltages of opposite polarities are applied to two opposite electrodes,respectively, of the four-piece electrode 29, one of the oppositeelectrodes expands and the other electrode contracts to bend thecylindrical tube. As a result, an end of the second scanner 26 moves inX direction indicated by an arrow 20 or Y direction indicated by anarrow 31.

The second scanner 26 is fixed to the housing 6 at its lower end and atits upper end, the optical fiber emission end 25 is fixed. For thisreason, the point source of light constituted by the optical fiberemission end 25 is movable in X, Y and Z directions. Such a movingoperation is controlled by the scanner control apparatus 48. Anoperation of the scanner control apparatus 48 will be described later.

Optical system constituting members including a lens 33, a polarizationbeam splitter 34, a quarter-wave plate 35, a prism 36, a light detectionmeans 37, a black plate 38, and a dichroic mirror transparent towavelength band of the light source 23 are fixedly provided to thehousing 6.

Measuring light emitted from the optical fiber emission end 25 isconverged by the lens 33 and enters the polarization beam splitter 34.Light reflected by the polarization beam splitter 34 is unnecessary,thus being absorbed by the black plate inclined with respect to theoptical axis. This is because even when light regularly reflected by thesurface of the black plate is generated, an influence thereof can beeliminated. On the other hand, light passing through the polarizationbeam splitter 34 passes through the quarter-wave plate 35 to beconverted into circularly polarized light. An optical axis of thecircularly polarized light is inclined by the prism 36 so that itcorresponds to a reflection surface of the probe 22.

The measuring light further passes through the dichroic mirror 39 and isfocused on a back surface side of the probe 22. In other words, aposition of the lens 33 is roughly adjusted so that the focus of lightis formed on the reflected surface of the probe 22.

As shown in FIG. 2( a), in order to form the focus on the probe 22, thepositions of the light source 23 and the probe 22 via the lens 33 mayprovide a conjugation relationship. More specifically, the followingrelationship (1) may be satisfied.

$\begin{matrix}{\frac{1}{f} = {\frac{1}{L\; 1} + \frac{1}{L\; 2}}} & (1)\end{matrix}$

wherein L1 represents a distance between the light source 23 and thelens 33, L2 represents a distance between the lens 33 and the probe 22,and f represents a focal length (distance) of the lens 33.

In this case, when the light source 23 is moved in X direction, thefocal length is moved in X direction at a ratio of L2:L1.

As described above, in this embodiment, the optical fiber emission end25 is used as the point source of light. The point source of light isfixed to the second scanner 26, so that it is possible to move the focusto a desired position by moving the second scanner 26.

The measuring light reflected by the probe 22 again passes through thedichroic mirror 39 and the prism 36 to change its direction so that theoptical axis is again parallel to Z axis. The light further passesthrough the quarter-wave plate 35, so that the circularly polarizedlight is reconverted into linearly polarized light. However, at thistime, a direction of the linearly polarized light is changed from thatof the original linearly polarized light by 90 degrees. For this reason,the linearly polarized light is reflected by the polarization beamsplitter 34 to enter the light detection means 37.

The light detection means 37 is a photodiode which is known as, e.g., afour-piece photodiode or a position sensor. The light detection means 37outputs current, from four electrodes, depending on a position ofincident light. The resultant signal is sent to an amplifier 45 for thelight detection means. The amplifier 45 converts the current signal fromthe photodiode into a voltage by a current-voltage conversion circuitand perform analog operation by an operational amplifier, so that thecurrent signal is finally converted into a light amount signal 46proportional to an amount of light entering the light detection means 37and a light position signal 47 representing a position of the center ofgravity of incident light.

When the probe 22 is bent, an angle of the reflected light is changed tomove the position of the center of gravity of light entering the lightdetection means 37. At this time, a degree of bending of the probe 22 isincreased by the movement of the position of the center of gravity, sothat the optical system functions as a so-called “optical lever”.Further, the bending of the probe 22 is caused by a force acting betweenthe member 1 to be measured and the probe 22, i.e., atomic force, sothat the light position signal 47 of the light detection means 37represents the atomic force.

The light amount signal 46 and the light position signal 47 are sent tothe scanner control apparatus 48. Incidentally, in order to reducenoises of the outputs from the light detection means 37, the lightamount signal 46, and the light position signal 47, the use of a lock-inamplifier is very effective. The lock-in amplifier is a device forselectively amplifying only a frequency component which has beendetermined in advance. A signal is modulated by a preliminarilydetermined frequency and a signal synchronized with the same frequencyis obtained by the lock-in amplifier. As a result, it is possible tosubstantially remove components other than the frequency component. Inthis case, the modulation is performed at a frequency at least ten timeshigher than a frequency of movement of the scanner. Assuming that ascanner characteristic is a two-dimensional system, vibration dampingcan be expected substantially on the order of the square of thefrequency. Thus, it is possible to prevent an increase in noise causedby the scanner operation. As the light modulation method, in addition tomodulation of light intensity of the light source, it is possible toemploy the above described AC mode, i.e., a method wherein thecantilever is vibrated at high frequency. In the former case, both ofthe light amount signal 46 and the light position signal 47 aremodulated, so that improvement in noise can be expected with respect toboth of the signals. In the latter case, the light position signal 47 ismodulated, so that the noise improvement can be expected with respect toonly the signal 47.

Further, a camera 43 and a black plate 44 are fixedly provided to thehousing 6. The dichroic mirror 39 reflects only light of a particularwavelength, so that it is possible to receive an image of the surface ofthe member to be measured by the camera 43 with the light of theparticular wavelength. On the other hand, light other than the light ofthe particular wavelength passes through the dichroic mirror 39.However, the black plate 44 is disposed on the optical axis, so that thelight passing through the dichroic mirror 39 do not enter the camera 43,thus being prevented from disturbing the image. The camera 43 isconnected to an unshown monitor on which the image is displayed.

Next, an operation of the scanner control apparatus 48 will bedescribed. This apparatus is constituted by a computer capable ofperforming high-speed operation and a drive amplifier for actuating thescanner and is capable of operating a plurality of control programs in amultitasking manner.

FIG. 5 is a control block diagram of the scanner control apparatus 48.

First, a feedback control system of bending of the probe 22 will bedescribed. As described above, the bending of the probe 22 is caused bythe force acting between the member 1 to be measured and the probe 22,i.e., the atomic force. For this reason, the light position signal 47 ofthe light detection means 37 represents the atomic force. A targetatomic force is determined in advance and a light position target value49 of corresponding to the target atomic force is determined.

From the light position signal 47, the determined light position targetvalue 49 is subtracted and fed back to the Z fine movement axis 18through a control system including a Z fine movement axis compensator 50and a Z fine movement axis driver amplifier 51. The Z fine movement axiscompensator 50 is required for keeping stably the feedback controlsystem. For example, PID control is known.

By this control system, it is possible to operate the Z fine movementaxis 18 of the first scanner 10 so as to cancel a change in lightposition signal 47. The light position signal 47 represents the atomicforce and the Z fine movement axis 18 changes a relative distancebetween the probe 22 and the member 1 to be measured. More specifically,by performing the feedback control, it is possible to measureinformation on a height at which the atomic force is a constant value.This measurement is performed by a so-called null-balance method (zeromethod).

By the control according to the null-balance method, the Z axis of thefirst scanner 10 is vertically moved along projections and recesses ofthe member 1 to be measured. When the vertical movement is large, theprobe 22 is largely moved in the optical axis direction of the “opticallever”. As a result, the focus is not formed on the probe, thusresulting in a large problem in a conventional method. According to thisembodiment, it is possible to adjust the position of the focus in theoptical axis direction in accordance with displacement of Z axis of thefirst scanner 10, so that the problem in the conventional method hasbeen solved as described later.

A target position 53 of XY scanning for scanning the entire measuringrange of the member 1 to be measured is created and the XY scanner 7 isdriven via the XY scanner driver amplifier 54.

Further, the position conversion data is preliminarily stored in astoring portion. The position conversion data is data for positionrelationship between the X, Y and Z positions of the first scanner 10having the Z fine movement axis 18 and corresponding positions of thesecond scanner 26. By satisfying the position relationship, the focusposition of the “optical lever” optical system coincides with theposition of the probe 22. A preparation method of the positionconversion data will be described later.

The position conversion data 52 and the position of the first substrate10, i.e., an output of the compensator 50 and the target position of theXY scanning are inputted into a position converter 55 and a resultantoutput is inputted into the scanner driver amplifier 56 to drive apiezoelectric actuator portion of the second scanner 26. The positionconverter 55 is a coordinate conversion processing device for convertingX, Y and Z positions as an input of the first scanner 10 into X, Y and Zpositions as an output of the second scanner 26 by using the positionconversion data 52.

The position conversion data 52 will be described more specifically.

The X, Y and Z positions of the first scanner 10 are represented by avector Xn, and those of the second scanner 26 are represented by avector Yn. Here, a subscript n is any one of 1, 2 and 3. For example,X₁, X₂ and X₃ represent X position, Y position and Z position of thefirst scanner, respectively. Coordinate conversion is effected accordingto the following formula (2):

$\begin{matrix}{Y_{m} = {\sum\limits_{i = 0}^{n}\; {\sum\limits_{j = 1}^{3}\; {c_{i,m,j}X_{j}^{i}}}}} & (2)\end{matrix}$

wherein m=1, 2 or 3 and a coefficient c_(i,j,m) represents the positionconversion data 52.

The formula (2) represents an input/output relationship as a powerpolynomial of n-th degree. According to the formula (2), it is possibleto perform such a conversion that a nonlinear component having thedegree of 2 or more is taken into consideration.

For example, a polynomial for correcting only offset and magnificationcan e realized by taking the degree as 1 and modifying the formula (2)into the following formula (3):

Y ₁ =c _(0,1,1) +c _(1,1,1) X ₁

Y ₂ =c _(0,2,2) +c _(1,2,2) X ₂

Y ₃ =c _(0,3,3) +c _(1,3,3) X ₃  (3)

Here, the offset means positional deviation between the focus positionof the “optical lever” and the probe position and is corrected by theabove formula (3), so that it is possible to cause the focus positionand the probe position to coincide with each other.

Further, the magnification means a ratio of an amount of movement of thefocus position moved by the second scanner 26 to an amount of movementof the first scanner 10 and is determined depending on a productionerror of mechanism parts or a magnification of the optical system forconverging light from the point of source of light fixed to the secondscanner 26 and focusing the light on the probe.

Further, in the case where the movement directions of the firstsubstrate 10 and the second substrate 26 are slightly inclined, byadding coefficients taking the inclination into consideration to theabove formula (3) to provide formula (4) shown below, it is possible tomake correction. The added terms represent rotating matrix.

Y ₁ =c _(0,1,1) +c _(1,1,1) X ₁ +c _(1,1,2) X ₂

Y ₂ =c _(0,2,2) +c _(1,2,1) X ₁ +c _(1,2,2) X ₂

Y ₃ =c _(0,3,3) +c _(1,3,3) X ₃  (4)

In a similar manner, it is also possible to make correction for a higherdegree.

The probe 22 includes a pointed portion 60 a for sensing atomic forcebetween it and the member 1 to be measured and a cantilever 60 bprovided with a trunk portion 60 c between the pointed portion 60 afixed thereto and the cantilever 60 b, as shown in FIG. 6( a).

In a conventional probe shown in FIG. 6( b), a pointed portion is short,so that the probe cannot follow a deep recessed shape. In this case, itis possible to meet the recessed shape by increasing a length of thepointed portion. However, a plate spring is bent, so that a change inattitude of the pointed portion is large. In view of this problem, inthis embodiment, the change in attitude of the pointed portion isdecreased by providing two parallel plate springs constituting thecantilever 60 b. Further, by providing the trunk portion 60 c forprolonging the pointed portion, an upper plate spring has a reflectionsurface. In the present invention, it is desirable that the probe havingsuch a plate spring structure is employed.

The measuring light is reflected by the reflection surface formed at anupper surface of the cantilever 60 b and the position of the probe 22 isautomatically detected while detecting an amount of light entering thelight detection means 37. By using a detection result, it is possible toeffect precise adjustment of the focus position.

FIG. 7 is a schematic view of the probe 22 as seen from above. A focus40 of the “optical lever” optical system is detected along a trace 41having a meander shape as shown in FIG. 7 by scanning with the secondscanner 26. An amount of light entering the light detection means 37 isincreased when the focus position is located on the probe 22 during thescanning. When a signal of the light amount is outputted as atwo-dimensional light amount (output) map, a position and shape of theprobe can be read. As a result, it is possible to determine an optimumposition (optimum focus position) for placing the focus 40 on the probe22. The optimum probe 42 is a position where the focus 40 coincides withthe reflection surface of the probe 22 to increase the amount of lightentering the light detection means 37 and is located in the neighborhoodof an end portion of the probe 22 to be largely bent.

A step of preparing the above described light amount map by effectingthe scanning with the second scanner 26 is repeated by changing theposition of the first scanner 10, whereby a table of the focus positioncorresponding to the position of the first scanner, i.e., the positionconversion data can be prepared. By using this table, the second scanner26 is controlled in synchronism with the first scanner 10, so that thefocus position is capable of being always kept at the optimum positionof the probe 22.

FIG. 8 shows the light amount map in this embodiment. An abscissarepresents the position of the second scanner 26 and an ordinaterepresents the light amount signal 46. A maximum of the light amount istaken as α1. A threshold is taken as α2 which is an appropriate valuenot more than α1, e.g., 90% of α1. By the threshold α2, it is possibleto draw a contour line as shown in FIG. 8. This contour line representsa contour of the probe 22. In the contour line, a point closest to theend of the probe 22 is taken as β. The position of β can be regarded asthe end of the probe 22. A point distant from the point β by a certainlength, e.g., equal to a spot size of light in a direction toward thefixed portion of the probe 22 is taken as the optimum position 42. Thisis because it is possible to obviate a large change in light amountcaused by even slight deviation of the position of the point β due to amovement error or the like of a scanning axis.

In a similar manner, it is possible to determine an optimum position inthe optical axis direction of the second scanner. When the probe 22 isdeviated in the optical axis direction, the reflected light is largelydiverged to lower the amount of light entering the light detection means37. A position at which the light amount is maximum is an optimum focusposition in the optical axis direction. It is possible to ensure asufficient amount of light by causing the focus of the optical system tofollow the optimum position determined in the above described manner.Further, the focus position is close to the end of the probe 22, so thatthe probe 22 is bent largely. As a result, a measurement sensitivity isadvantageously high.

However, the “optical lever” optical system has a small NA (numericalaperture), so that it is less sensitive to deviation in the optical axisdirection and has a considerable depth of focus. For this reason, in thecase where the deviation in the optical axis direction is small, the“optical lever” optical system is sufficiently practical even whencontrol in the optical axis direction is omitted.

In the conventional technique, it has been difficult to detect theoptimum focus position but in this embodiment, it is possible to detectthe optimum position on the probe by monitoring an amount of light ofthe light detection means 37 while effecting scanning of the focus withthe second scanner 26. Further, in the conventional technique,adjustment of the focus position has been complicated but in thisembodiment, it is possible to always keep the focus position at theoptimum position on the probe by preparing a table (position conversiondata) of the optimum focus position and controlling the second scanner26 in correspondence with the position of the first scanner 10 by meansof the table. Further, in the conventional technique, alignmentadjustment during replacement of the probe has been complicated butaccording to this embodiment, it is possible to simply meet thealignment adjustment since the detection of the focus position and theadjustment of the focus position can be automatically performed.

FIG. 9 is a flow chart for explaining a method of obtaining the positionconversion data 52.

In the case where the degree of position conversion by the polynomial isincreased, the number of the position conversion data 52 as acoefficient of the formula (2) described above is increased. Further,the coefficient includes factors, which are not determinedtheoretically, such as a production error of mechanism parts and anadjustment error of the optical system, thus requiring measurement.

First, the position conversion data 52 is initialized in step 100. Itcan be considered that the second scanner 26 cannot be actuated at allwhen an abnormal value is set as the position conversion data 52. Forthis reason, the position conversion data 52 is first initialized. Asthe initial value, it is possible to use a simple model represented bythe above described formula (3). At this stage, it is not necessary thatthe position conversion data 52 is accurate, so that the theoreticalstudy result represented by the formula (3) is sufficient.

In step 101, the Z(-axis) coarse movement stage 5 is moved upward, sothat the member 1 to be measured is separated from the probe 22. In step102, a position of the first scanner 10 is selected from a measuringarea. The measuring area is divided into an finite number of lattices.Each of lattice points is successively selected and the first scanner 10is moved to a position of the selected lattice point. In step 103, theoptical system is subjected to scanning with the second scanner 26 tomeasure and obtain a map of the light amount signal 46.

In step 104, it is confirmed that the light amount is in a normal range.When the light amount is in an abnormal range, the procedure isterminated due to error. In the case where the entire light amount maphas an insufficient light amount, error termination is effected since itis considered that alignment of the “optical lever” optical system islargely deviated or that the probe is detached from the fixed portion.In step 105, an optimum position on which the focus is placed isdetermined from the light amount map. As shown in FIG. 8, it is possibleto read the position and the shape of the probe 22 from the light amountmap, so that it is possible to obtain the optimum position 42 at whichthe focus 40 is optimally placed on the probe 22.

In step 106, when the entire measuring area is not covered completely,the first scanner is moved to a next position and the procedure isreturned to step 102.

By this loop, a position of the second scanner 26 corresponding to aposition of the first scanner 10 in order to realize the optimum focusposition in the finite number of lattice points is obtained. This issets of pairs of inputs and outputs, i.e., X and Y, represented by theabove described formula (2).

In step 107, the position conversion data 52 is calculated. Morespecifically, by using the sets of pairs of inputs and outputsrepresented by formula (2), a coefficient is calculated according to themethod of least squares. The formula (2) is a model for the polynomial,so that when residual error is large, accuracy can be improved byincreasing the degree of the polynomial. The thus obtained coefficientis the position conversion data 52.

By using the above obtained position conversion data 52, the position ofthe second scanner 26 is controlled in correspondence with the positionof the first scanner 10, so that it is possible to always keep the focusposition at the optimum position of the probe 22.

In this embodiment, a search for the probe position is made byperforming scanning with the second scanner 26. Similarly, it is alsopossible to obtain the position conversion data 52 by making the searchfor the probe position by performing scanning with the first scanner 10.

FIG. 10 shows a flow chart of a measuring operation of the atomic forcemicroscope.

First, in step 200, the 8 coarse movement stage 5 is moved upward andthe member 1 to be measured is set to the XY coarse movement stage 2. Instep 201, it is confirmed that the light amount signal 46 of the lightdetection means 37 is in a normal range. When the light amount signal 46is in an abnormal range, the procedure is terminated due to error. Forexample, in the case where the light amount is insufficient, errortermination is effected since it is considered that initial settingerror such that alignment of the “optical lever” optical system isdeviated or that the probe 22 is detached from the fixed portion iscaused to occur. Further, in the former case (alignment deviation), bysetting the position conversion data 52 again in accordance with theabove described procedure, it is possible to effect measurement again.

In step 202, it is confirmed that the light position signal 47 of thelight detection means 37 is in a normal range. When the light positionsignal 47 is in an abnormal range, error termination is effected. Thelight position signal 47 represents bending of the probe 22 enlarged bythe action of the “optical lever”. In the case where the light positionsignal 47 is abnormally larger than a preliminarily determinedthreshold, error termination is effected since it is considered that theprobe 22 is largely bent originally.

In step 203, offset of the light position signal 47 of the lightdetection means 37 is set so that an output is zero. In a state in whichthe probe 22 and the member 1 to be measured are apart from each other,the offset of the light position signal 47 is effected in order tocancel minute alignment error of the “optical lever” optical system andoffset error of an electrical system. In step 204, the Z coarse movementstage 5 is moved until the light position signal 47 reaches apreliminarily set value. The light position signal 47, as describedabove, represents the bending of the probe 22 enlarged by the action ofthe “optical lever”, i.e., a force acting between the probe 22 and themember 1 to be measured. The Z coarse movement stage 5 is moved upwardand downward until the force reaches the preliminarily set value. As aresult, the probe 22 is brought very close to the member 1, so that aninfluence of atomic force is shown.

In step 205, feedback control is effected with respect to the Z finemovement axis 18 so that an output of the light position signal 47 isconstant. By this feedback control, as described above, it is possibleto perform measurement according to the null-balance method. When thefeedback control is effected, the force acting between the probe 22 andthe member 1 to be measured is constant, so that the Z coarse movementstage 5 is moved upward and downward depending on projections andrecesses of the member 1.

In step 206, scanning with the first scanner 10 is effected in themeasuring range. In the measuring range, scanning with the probe 22 iseffected to record the light position signal 47 and the position of theZ fine movement axis 18 in the entire measuring range. At that time, asdescribed above with reference to the block diagram shown in FIG. 5, theposition of the second scanner 26 is controlled in correspondence withthe position of the first scanner 10, i.e., the positions of the Z finemovement axis 18 and the XY scanner 7, by using the position conversiondata 52. By this control, the focus of the “optical lever” opticalsystem always follows the surface of the probe 22.

In step 207, a measurement result is calculated displayed, and stored.The measurement result is shown in a graph having an abscissarepresenting XY position of the first scanner 10 and an ordinaterepresenting a position of the Z fine movement axis 18.

With respect to the Z fine movement axis 18, feedback control iseffected so that the light position signal 47 representing the forceexerted between the probe 22 and the member 1, i.e., atomic force isconstant. Accordingly, the measurement result represents projections andrecesses of the member 1 providing a constant atomic force.

In the feedback control, control error (system deviation) occurs evenwhen a degree of the control error is slight. Even when there is thecontrol error, it is possible to make correction by adding a valueobtained by converting an output of the light position signal 47 intodisplacement in Z direction to a measured value. A conversion ratio atthis time is a ratio between an amount of movement of the member 1 to bemeasured and an amount of movement of the light position signal 47. Thisratio can be measured by gradually pushing the probe 22 into the member1 in the apparatus shown in FIG. 1. Further, it is also possible tocalculate the ratio by using a computational model of atomic force.

In step 208, the Z coarse movement stage 5 is moved upward and themember 1 to be measured is detached from the XY coarse movement stage 2.

According to this embodiment, it is possible to always place the focusposition on the probe 22 by adjusting the focus position incorrespondence with the position of the first scanner 10 by means of thesecond scanner 26 although it has been difficult to effect high-accuracymeasurement in the conventional technique since the positions of thefocus and the probe are inevitably deviated from each other.

Further, in JP-A Hei 5-312561 described above, the end of the probescanner cannot be reduced in size, so that it has been difficult toperform measurement with high accuracy. However, in this embodiment, thelight source is not required to be disposed at the end of the probescanner, so that the probe end can be reduced in size.

Further, in the conventional technique, it has been difficult to effectthe high-accuracy measurement since it is impossible to prevent thedeviation in the optical axis direction of the probe. However, accordingto this embodiment, it is possible to adjust a three-dimensionalposition of the focus as described above, so that it is possible toprevent the deviation in the optical axis direction. Further, bymonitoring the light amount of the light detection means with the secondscanner, it is possible to detect the optimum focus position.

In the conventional technique, adjustment of the focus position has beencomplicated but according to this embodiment, it is possible to alwayskeep the focus position at an optimum portion for the probe by preparinga table for the optimum focus position and controlling the position ofthe second scanner in correspondence with the first scanner by means ofthe table.

In the conventional technique, alignment adjustment during replacementof the probe has been complicated. However, according to thisembodiment, an operation or judgement by an operator is not required fordetection of the focus position and adjustment of the focus position, sothat the alignment adjustment can be performed automatically, thus beingeffected simply.

Incidentally, a basic function of the optical system is not changed evenwhen the order of arrangement of optical members constituting theoptical system is changed. In this embodiment, these members aredisposed in the order of the light source, the lens, the polarizationbeam splitter, the quarter wave plate, the prism, and the dichroicmirror. It has been known that a transmission intensity of light beamentering the surface of a dielectric member in a state in which thelight beam inclines with respect to the dielectric member surface variesdepending on a direction of the polarized light. The circularlypolarized light passing through the quarter-wave plate and entering theprism is changed to elliptically polarized light by the above effect.Thus, the light beam reflected by the probe and entering thequarter-wave plate is changed to the elliptically polarized light.Accordingly, light which is not returned to the linearly polarized lightis slightly generated and passes through the polarization beam splitter,thus being returned to the light source side. This light is unnecessarystray light, so that there is a possibility that the light lead stopnoise. For this reason, the positions of the wave plate and the prismmay be replaced with each other, whereby the above possibility can beeliminated since the influence of the inclined surface of the prism isremoved.

In this embodiment, the “optical lever” optical system is disposed onthe transmission side of the dichroic mirror and the camera is disposedon the reflection side but a similar effect can be achieved even whenthe positions of these members are changed to each other. Further, inthis embodiment, the first scanner is constituted by the combination ofthe XY scanner and the Z fine movement axis but a similar effect can beobtained even when the first scanner is constituted by the tube scanner.Similarly, the similar effect can also be achieved even when the secondscanner is constituted by the combination of the XY scanner and the Zfine movement axis.

Further, in this embodiment, the emission end of the optical fiber asthe point source of light is fixed to the second scanner but it is alsopossible to realize a similar function even when the lens is moved orthe light source and the lens are simultaneously moved.

In this embodiment, it is preferable that an output signal of the lightdetection means is sent to the lock-in amplifier and a synchronizingfrequency of the lock-in amplifier is at least 10 times an operatingfrequency of the scanner. In order to effect the high-accuracymeasurement, it is important to take various countermeasures againstdisturbance. As a large noise source, factors such as a change in lightamount of illumination light for the measuring apparatus and vibrationand electrical noise in synchronism with the operation of the scannercan be considered. These noises are alleviated by modulating a signalwith a preliminarily set frequency and utilizing only thefrequency-modulated signal. When the signal-modulating frequency is setto be at least 10 times the operating frequency of the scanner, it ispossible to considerably alleviate the influence of the noises caused bymovements of the first and second scanners. For example, assuming thatthe characteristic of the scanner is a two-dimensional system which isan ordinary mechanical characteristic, when the frequency is increasedby 10 times the operating frequency of the scanner, response to the samedisturbance is attenuated so as to be about 1/100. When the frequency isfurther increased, it is possible to move effectively attenuate theresponse.

Further, as means for modulating the signal, a similar function isrealized by employing, e.g., a method of modulating a light intensity ofthe light source, a method using the second scanner as a focus positionmoving means, a method vibrating the probe, etc.

In this embodiment, the focus is formed on the reflection surface of theprobe. However, in an actual optical system, the position of the focusis a position of beam waist, is that the focus does not mean amathematical point.

Embodiment 2

FIG. 11 illustrates an atomic force microscope according to Embodiment2. The atomic force microscope of this embodiment has the sameconstitution as that of the atomic force microscope of Embodiment 1except that an auto focus apparatus is incorporated in an optical pathof reflected light from the probe 22.

The auto focus apparatus is fixed to the housing and includes a halfmirror 58, a lens 59, a cylindrical lens 61, and a four-piece photodiode62.

Light reflected by the probe 22 is diffusive light since focus thereofis placed on the probe 22. The light is reflected by the beam splitter34 and enters the half mirror 58. The transmitted light enters the lightdetection means 37 and the reflected light is converted into lightconverged by the lens 59 and passes through the cylindrical lens 61 toenter the four-piece photodiode 62.

The auto focus apparatus utilizing astigmatism described aboveintroduces therein light branched by the half mirror disposed in theoptical path of the light reflected by the reflection surface of theprobe. In addition to the light amount map, by using an output of theauto focus apparatus, a position of the probe is calculated. Also in theoptical axis direction, the light reflected by the probe diffuses, sothat the amount of light entering the light detection means isdecreased. For this reason, similarly as in the case of the directionperpendicular to the optical axis, an optimum position can be searchedwhile detecting the light amount. However, the NA of the “optical lever”optical system is small, so that the optical system is less sensitive todeviation in the optical axis direction, i.e., has a large depth offocus. Accordingly, the deviation in the optical axis directiondetectable by the light amount of the light detection means is low insensitivity.

In this embodiment, the light reflected by the probe is branched by thehalf mirror and deviation thereof in the optical axis direction isdetected by the auto focus apparatus. The auto focus apparatus has sometypes but the auto focus apparatus utilizing the astigmatism as shown inFIGS. 12 and 13 has been widely used.

Referring to FIG. 12, the light reflected by the probe is diffused, sothat it is first converted into converging light. When the light passesthrough the cylindrical lens 62, strong astigmatism is generated. F1represents a focus position at which light is converged by the action ofthe lens alone. In this embodiment, the focus position F1, a lightintensity distribution is extended in a lateral (horizontal) directionby the influence of the cylindrical lens 61. F3 represents a compositefocus of the lens 59 and the cylindrical lens 61. At this position, alight intensity distribution is extended in a vertical direction. At aposition of F2 which is an intermediary position between F1 and F3, alight intensity distribution assumes a circular shape with a balancebetween those at the positions of F1 and F2.

FIG. 13 shows light intensity distributions at a light-receiving surfaceof the four-piece photodiode 62 at the positions of F1, F2 and F2. Atthe position of F1, the light intensity distribution is extendedlaterally, so that two signals from left and right diodes of four diodesare stronger than those from upper and lower diodes. At the position ofF2, the circular light intensity distribution is created, so that anoutput from each of the four diodes is identical to each other. Further,at the position of F3, two signals from the upper and lower diodes arestronger than those from the right and left diodes.

Thus, by using the four-piece photodiode 62, it is possible to detectthat the position of the focus is deviated in what direction. The autofocus apparatus used in this embodiment is capable of providing highaccuracy in a method in which deviation of the focus in the optical axisdirection is detected only by the light intensity.

Accordingly, by measuring the deviation in the optical axis directionusing the auto focus apparatus in addition to measurement of thedeviation in the direction perpendicular to the optical axis using thelight amount of the light detection means 37, it is possible to obtainthe position conversion data also in the optical axis direction withhigh accuracy.

As described above, the measurement accuracy is improved even withrespect to the deviation in the optical axis direction by the auto focusapparatus, so that it is possible to cause the focus position toaccurately coincide with the probe position. As a result, themeasurement accuracy can be further improved. In addition, it is alsopossible to obtain the position conversion data in all the directionswith high accuracy.

As described above, in the case where the measurement according to thenull-balance method in which the feedback control is effected withrespect to the Z fine movement axis so that the force, due to thebending of the probe, acting between the probe and the member to bemeasured is constant, the probe is moved upward and downward dependingon projections and recesses of the surface of the member to be measured.By this upward and downward movement of the probe, the focus position ofthe “optical lever” optical system is also deviated in the optical axisdirection. However, in this embodiment, it is possible to obtain theposition conversion data also in the optical axis direction with highaccuracy, so that it is possible to correct the deviation in the opticalaxis direction with high accuracy. Particularly, a roughened surface issubjected to measurement, displacement of the Z fine movement axis ofthe probe is large. For this reason, the technique of this embodiment isvery important.

Embodiment 3

FIG. 14 illustrates an atomic force microscope according to Embodiment3. The atomic force microscope of this embodiment has the sameconstitution as that of the atomic force microscope according toEmbodiment 1 except that galvano-mirrors 71 and 72 are incorporatedtherein in an optical path of reflected light from the probe 22.

The galvano-mirror has been widely used as a light polarizing devicecapable of controlling an angle of a mirror at high speed by utilizingelectromagnetic force etc. It is also possible to control the directionof light in two directions by combining two galvano-mirrors each capableof controlling one angle of rotation. Further, by disposing a planargalvano-mirror using a torsion bar in the optical system, the focusposition can be moved at high speed.

In this embodiment, a light source 23 such as a semiconductor laser isprovided fixedly to the housing 6 so that emitted light is guided intothe optical fiber 24. The emission end 25 of the optical fiber, i.e., apoint source of light is fixed to the housing 6, so that converginglight ray is obtained by the lens 33 fixed also to the housing 6. Thetwo galvano-mirrors 71 and 72 are provided fixedly to the housing 6 andwhen the conversing light ray is reflected by the two galvano-mirrors 71and 72, it is possible to change the direction of this light ray.

The galvano-mirror is a device for controlling an angle of a mirrorreduced in size and weight utilizing electromagnetic force or the like,e.g., a device having such a structure that a mirror is fixed to arotational axis of a servomotor. By employing the small-size mirror anda high-output motor, it is possible to change the direction of the lightray at high speed.

By adjusting the angle of the galvano-mirrors, the direction of thelight ray is changed, so that the focus position can be changed.

In this embodiment, the galvano-mirrors are used, so that compared withEmbodiment 1, it is possible to effect higher speed scanning of thefocus position. Accordingly, it is possible to realize an atomic forcemicroscope with shorter measuring time.

In this embodiment, the galvano-mirror including the mirror constitutedby the rotation-type servomotor is used but may also be constituted byusing a torsion lever prepared by processing a silicon wafer.

Further, in this embodiment, the mirrors are disposed between the lens33 and the polarization beam splitter 34 but may also be disposed at anyposition so long as they are located in the optical path. For example, asimilar function of changing the focus position is achieved by disposingthe mirrors between the prism 36 and the probe 22.

Embodiment 4

FIG. 15 illustrates an atomic force microscope according to Embodiment4. The atomic force microscope of this embodiment has the sameconstitution as that of the atomic force microscope according toEmbodiment 1 except that the lens 33 is fixed to the end of the secondscanner 26.

The emission end 25 of the optical fiber is fixedly provided to thehousing 6 and the second scanner 26 is fixedly provided to the opticalfiber emission end 25 at an upper end thereof. At a lower end of thesecond scanner 26, the lens 33 is fixedly provided.

In the constitution of this embodiment, by the operation of the secondscanner 26, it is possible to move X, Y and Z positions of the lens 33.When the lens 33 is moved in a direction perpendicular to the opticalaxis direction, the focus position is also moved in the directionperpendicular to the optical axis direction. Further, when the lens 33is moved in the optical axis direction, the focus position is also movedin the optical axis direction. Accordingly, the X, Y and Z positions ofthe focus position can be controlled by the second scanner 26.

Embodiment 5

FIG. 16 illustrates an atomic force microscope according to Embodiment5. The atomic force microscope of this embodiment has the sameconstitution as that of the atomic force microscope according toEmbodiment 1 except that the optical fiber emission end 25 and the lens33 are fixed to a member provided at an upper end of the second scanner26.

The second scanner 26 is fixedly provided to the housing 6 at a lowerend thereof. At the upper end of the second scanner 26, a body tubemember 63 is fixed. At both ends of the body tube member 63, the opticalfiber emission end 25 and the lens 33 are fixedly provided,respectively.

In the constitution of this embodiment, by the operation of the secondscanner 26, it is possible to move the X, Y and Z positions of the lens33 and the optical fiber emission end 25 as the point source of light atthe same time. As a result, it is possible to control the X, Y and Zpositions of the focus by the second scanner 26.

Embodiment 6

FIGS. 17 to 23 illustrate Embodiment 6, wherein FIG. 17 shows an atomicforce microscope according to this embodiment. The atomic forcemicroscope of this embodiment has the same constitution as that of theatomic force microscope according to Embodiment 1 except that the(single) probe 22 is changed to a probe assembly including a pluralityof probes 22 a to 22 c. In this embodiment, three probes are used butthe number thereof is not limited.

Each of the three probes 22 a, 22 b and 22 c has a beam-like structurehaving a very small thickness of several microns or below and a width ofseveral tens of microns in order to measure a very small force. Theseprobes are ordinarily prepared as a probe assembly having an integralstructure using photolithography.

The scanner control apparatus 48 is constituted by a computer capable ofeffecting high-speed processing and a driver amplifier for driving(operating) the respective scanners 10 and 26 and is capable ofoperating a plurality of control programs in a multitask manner.

FIG. 18 shows the probe assembly including the plurality of probes 22 ato 22 c (three probes in this embodiment). As described above, thenumber of the probes is not limited to three.

Independently of the probe assembly moved by the first scanner 10, it ispossible to move the focus position of the “optical lever” opticalsystem to a desired position by the second scanner 26. For this reason,a timing signal for successively repeating three states corresponding tothe three probes 22 a to 22 c is generated and the focus position iscontrolled by the timing signal. As a result, the focus 40 issuccessively placed on optimum positions 42 a, 42 b and 42 c of theprobes 22 a, 22 b and 22 c, respectively.

At this time, the light ray reflected from the respective probes 22 a to22 c enter the light detection means 37 and provide a single outputsignal. For this reason, in this embodiment, the output signal of thelight detection means 37 is divided into output signals corresponding tothe respective probes 22 a to 22 c in synchronism with the abovedescribed timing signal by means of a sample-and0hold device for holdingthe output signal of the light detection means 37.

When a switching speed of the timing signal is sufficiently high, it ispossible to apparently realize the same function as a combination of aplurality of light sources, optical systems, and light detection meansin correspondence with the plurality of probes. In other words, it ispossible to measure bending of each of the probes and permitsimultaneous measurement at several points, i.e., multiprobing.

Independently of the probe assembly moved by the first scanner 10, bymoving the focus position of the “optical lever” optical system by meansof the second scanner 26, it is possible to place the focus on theoptimum positions 42 a, 42 b and 42 c of the probes 22 a, 22 b and 22 c,respectively.

FIG. 19 is a schematic view of the three probes 22 a to 22 c as seenfrom above. When the focus is subjected to scanning with the secondscanner 26 along a meander scanning trace, the light amount of the lightdetection means 37 is increased when the focus 40 coincides with any oneof the probes. In such a state, a light amount map having an abscissarepresenting a position of the second scanner 26 and an ordinaterepresenting a light amount signal is created by measurement.

FIG. 20 shows a control block diagram for realizing multiprobing. Thiscontrol can be realized by the scanner control apparatus 48. A timingsignal generation apparatus 65 generates two timing signals, withdifferent times, including a multiplexer timing signal 66 and a sampletiming signal 67.

FIG. 21 is a time chart for the control. Referring to FIG. 21, themultiplexer timing signal 66 is a signal for periodically repeatingthree states corresponding to the three probes 22 a to 22 c and is sentto a multiplexer apparatus 68. The multiplexer apparatus 68 selects andoutputs one of inputted signals and the selected inputted signal can becontrolled by the multiplexer timing signal 66. To inputs of themultiplexer apparatus 68, three position conversion data 52 a, 52 b and52 c are connected. One of output data is sent to a position converter55. The three position conversion data 52 a, 52 b and 52 c correspondsto the optimum positions 42 a, 42 b and 42 c of the probes 22 a, 22 band 22 c, respectively.

The optimum positions 42 a, 42 b and 42 c and the corresponding positionconversion data 52 a, 52 b and 52 c are preliminarily measured andobtained as described later.

The position converter 55 is connected to a second scanner driveramplifier 56 and further connected to the second scanner 26.

As a result, the focus 40 is moved, by the second scanner 26, to theoptimum positions 42 a, 42 b and 42 c successively selected by themultiplexer timing signal 66.

Even when the probe assembly is moved by the first scanner 10, thesecond scanner 26 is moved synchronously to cause the focus 40 to followthe optimum position of the selected probe. As a result, as shown in thetime chart shown in FIG. 21, the light amount signal 46 and the lightposition signal 47 are outputted at the time when the focus is placed oneach of the probes 22 a to 22 c.

On the other hand, the sample timing signal 67 is a signal delayed by asmall waiting time δ from the multiplexer timing signal 66 and is sentto two sample-and-hold devices 69 a and 69 b.

Each of the sample-and-hold devices 69 a and 69 b effects asample-and-hold operation in which sampling is effected by dividing aninput signal into three signals and the sampled signal is held untilsubsequent sampling and then is outputted. The operation timing can becontrolled by the sample timing signal 67.

The waiting time δ corresponds to a delay of time from movement of thesecond scanner 26 is correspondence with the multiplexer timing signal66 to cause the light reflected by the probe to enter the lightdetection means 37 to output of the light amount signal 46 and the lightposition signal 47. As shown in the time chart of FIG. 21, the lightposition signal 47 starts a change at a timing of the multiplexer timingsignal 66 and at the time when the waiting time δ has elapsed tostabilize the signal, the sample-and-hold operation is performed by thesample timing signal 67.

When a switching speed of the timing signal generation apparatus 65 issufficiently high, it is possible to apparently realize the samefunction as a combination of a plurality of light sources, opticalsystems, and light detection means in correspondence with the pluralityof probes 22 a to 22 c. In other words, according to this embodiment, itis possible to measure bending of each of the probes 22 a to 22 c andpermit simultaneous measurement at several points, i.e., multiprobing.

The light position signal 47 is inputted into the sample-and-hold device69 a and is divided into three light position signals 47 a, 47 b and 47c corresponding to the three probes 22 a, 22 b and 22 c, respectively.

The light amount signal 46 is inputted into the sample-and-hold device69 b and is divided into three light amount signals 46 a, 46 b and 46 ccorresponding to the three probes 22 a, 22 b and 22 c, respectively.

First, a feedback control system of bending of the probe will bedescribed. As described above, the bending of the probe is caused by theforce acting between the member 1 to be measured and the probe 22, i.e.,the atomic force. For this reason, the light position signal 47 of thelight detection means 37 represents the atomic force. A target atomicforce is determined in advance and a light position target value 49 ofcorresponding to the target atomic force is determined. Then, one of thethree (divided) light position signals is selected. In this embodiment,description will be made by selecting the light position signal 47 bcorresponding to the central probe 22 b as an example. Even when otherprobes are selected, a similar result is achieved.

From the selected light position signal 47 b, the light position targetvalue 49 is subtracted and fed back to the Z fine movement axis 18through a control system including a Z fine movement axis compensator 50and a Z fine movement axis driver amplifier 51. The Z fine movement axiscompensator 50 is required for keeping stably the feedback controlsystem. For example, PID control is known.

As described above, when one signal is selected, the same control as inthe case of the single probe is effected.

By this control system, the Z fine movement axis 18 of the first scanner10 is separated so as to cancel a change in light position signal 47 b.The light position signal 47 b represents the atomic force and the Zfine movement axis 18 changes a relative distance between the probe 22 band the member 1 to be measured. More specifically, by performing thefeedback control, it is possible to measure information on a height atwhich the atomic force is a constant value. This measurement isperformed by the null-balance method (zero method).

By the control according to the null-balance method, the Z axis of thefirst scanner 10 is vertically moved along projections and recesses ofthe member 1 to be measured. When the vertical movement is large, theprobe is largely moved in the optical axis direction of the “opticallever”. As a result, the focus is not formed on the probe, thusresulting in a large problem in a conventional method. According to thisembodiment, it is possible to adjust the position of the focus in theoptical axis direction in accordance with displacement of Z axis of thefirst scanner 10, so that the problem in the conventional method hasbeen solved.

A target position 53 of XY scanning for scanning the entire measuringrange of the member 1 to be measured is created and the XY scanner 7 isdriven via the XY scanner driver amplifier 54.

Further, the position conversion data 52 a, 52 b and 52 c correspondingto the three probes 22 a, 22 b and 22 c are preliminarily prepared. Eachof the position conversion data represents a position relationshipbetween the X, Y and Z positions of the first scanner 10 having the Zfine movement axis 18 and corresponding positions of the second scanner26. By satisfying the position relationship, the focus position of the“optical lever” optical system coincides with the position of the probe.A preparation method of the position conversion data 52 a, 52 b and 52 cwill be described later.

One of the three position conversion data 52 a, 52 b and 52 c isselected in synchronism with the timing signal 66 by using themultiplexer 68.

The selected position conversion data 52 b and the position of the firstsubstrate 10, i.e., an output of the compensator 50 and the targetposition of the XY scanning are inputted into a position converter 55and a resultant output is inputted into the scanner driver amplifier 56to drive the second scanner 26.

After one probe is selected by the multiplexer 68, the positionconversion data 52 b and the operation of the position converter 55 areidentical to those in Embodiment 1, thus being omitted from thefollowing description.

FIG. 22 is a flow chart for obtaining the position conversion data 52 ato 52 c for the atomic force microscope of this embodiment.

First, the position conversion data 52 a to 52 c are initialized,respectively in step 110. It can be considered that the second scanner26 cannot be actuated at all when an abnormal value is set as each ofthe position conversion data 52 a to 52 c. For this reason, each of theposition conversion data 52 a to 52 c is first initialized. As theinitial value, it is possible to use a simple model represented by theabove described formula (2). At this stage, it is not necessary thateach of the position conversion data 52 a to 52 c is accurate, so thatthe theoretical study result represented by the formula (2) issufficient.

In step 111, the Z(-axis) coarse movement stage 5 is moved upward, sothat the member 1 to be measured is separated from the probe assembly.In step 112, a position of the first scanner 10 is selected from ameasuring area. The measuring area is divided into an finite number oflattices. Each of lattice points is successively selected and the firstscanner 10 is moved to a position of the selected lattice point. In step113, the optical system is subjected to scanning with the second scanner26 to measure and obtain a map of the light amount signals 46 a to 46 c.

In step 114, it is confirmed that the light amount is in a normal range.When the light amount is in an abnormal range, the procedure isterminated due to error. In the case where the entire light amount maphas an insufficient light amount, error termination is effected since itis considered that alignment of the “optical lever” optical system islargely deviated or that the probe assembly is detached from the fixedportion. In step 115, an optimum position on which the focus is placedis determined from the light amount map. It is possible to read theposition and the shape of the probes 22 a to 22 c from the light amountmap, so that it is possible to obtain the optimum positions 42 a to 42 cat which the focus 40 is optimally placed on the reflected surfaces ofthe probes 22 a to 22 c as shown in FIG. 19.

In step 116, when the entire measuring area is not covered completely,the first scanner is moved to a next position and the procedure isreturned to step 112.

By this loop, a position of the second scanner 26 corresponding to aposition of the first scanner 10 in order to realize the optimum focusposition in the finite number of lattice points is obtained. This issets of pairs of inputs and outputs, i.e., X position and Y position,represented by the above described formula (2).

In step 117, the position conversion data 52 a to 52 c are calculated.More specifically, by using the sets of pairs of inputs and outputsrepresented by formula (2), each of coefficients is calculated accordingto the method of least squares. The formula (2) is a model for thepolynomial, so that when residual error is large, accuracy can beimproved by increasing the degree of the polynomial. The thus obtainedcoefficients are the position conversion data 52 a to 52 c.

FIG. 23 shows a flow chart of an entire measuring operation of theatomic force microscope.

First, in step 210, the 8 coarse movement stage 5 is moved upward andthe member 1 to be measured is set to the XY coarse movement stage 2. Instep 211, it is confirmed that the light amount signal 46 of the lightdetection means 37 is in a normal range. When the light amount signal 46is in an abnormal range, the procedure is terminated due to error. Forexample, in the case where the light amount is insufficient, errortermination is effected since it is considered that initial settingerror such that alignment of the “optical lever” optical system isdeviated or that the probe assembly is detached from the fixed portionis caused to occur. Further, in the former case (alignment deviation),by setting the position conversion data 52 a to 52 c again in accordancewith the above described procedure, it is possible to effect measurementagain.

In step 212, it is confirmed that the light position signal 47 of thelight detection means 37 is in a normal range. When the light positionsignal 47 is in an abnormal range, error termination is effected. Thelight position signal 47 represents bending of the probes 22 a to 22 cenlarged by the action of the “optical lever”. In the case where thelight position signal 47 is abnormally larger than a preliminarilydetermined threshold, error termination is effected since it isconsidered that the probes 22 a to 22 c are largely bent originally.

In step 213, offset of the light position signal 47 of the lightdetection means 37 is set so that an output is zero. In a state in whichthe probe assembly and the member 1 to be measured are apart from eachother, the offset of the light position signal 47 is effected in orderto cancel minute alignment error of the “optical lever” optical systemand offset error of an electrical system. In step 214, the Z coarsemovement stage 5 is moved until the light position signal 47 reaches apreliminarily set value. The light position signal 47, as describedabove, represents the bending of each of the probes 22 a to 22 cenlarged by the action of the “optical lever”, i.e., a force actingbetween each of the probes 22 a to 22 c and the member 1 to be measured.The Z coarse movement stage 5 is moved upward and downward until theforce reaches the preliminarily set value. As a result, the probeassembly is brought very close to the member 1, so that an influence ofatomic force is shown.

In step 215, feedback control is effected with respect to the Z finemovement axis 18 so that an output of the light position signal 47 isconstant. By this feedback control, as described above, it is possibleto perform measurement according to the null-balance method. When thefeedback control is effected, the force acting between each of theprobes 22 a to 22 c and the member 1 to be measured is constant, so thatthe Z coarse movement stage 5 is moved upward and downward depending onprojections and recesses of the member 1.

In step 216, scanning with the first scanner 10 is effected in themeasuring range. In the measuring range, scanning with the probeassembly is effected to record the light position signal 47 and theposition of the Z fine movement axis 18 in the entire measuring range.At that time, as described above with reference to the block diagramshown in FIG. 20, the position of the second scanner 26 is controlled incorrespondence with the position of the first scanner 10, i.e., thepositions of the Z fine movement axis 18 and the XY scanner 7, by usingthe position conversion data 52 a to 52 c. By this control, the focus 40of the “optical lever” optical system always follows the surfaces of theprobes 22 a to 22 c. Further, the position conversion data 52 a to 52 care switched by the timing signal 66, so that the focus is successivelymoved on the respective probes 22 a to 22 c.

In step 217, a measurement result is calculated displayed, and stored.The measurement result is shown in a graph having an abscissarepresenting XY position of the first scanner 10 and an ordinaterepresenting a position of the Z fine movement axis 18.

With respect to the Z fine movement axis 18, feedback control iseffected so that the light position signal 47 representing the forceexerted between each of the probes 22 a to 22 c and the member 1, i.e.,atomic force is constant. Accordingly, the measurement result representsa map of projections and recesses of the member 1 providing a constantatomic force.

In the feedback control, control error (system deviation) occurs evenwhen a degree of the control error is slight. Even when there is thecontrol error, it is possible to make correction by adding a valueobtained by converting an output of the light position signal 47 intodisplacement in Z direction to a measured value. A conversion ratio atthis time is a ratio between an amount of movement of the member 1 to bemeasured and an amount of movement of the light position signal 47. Thisratio can be measured by gradually pushing the probes 22 a to 22 c intothe member 1. Further, it is also possible to calculate the ratio byusing a computational model of atomic force.

In step 218, the Z coarse movement stage 5 is moved upward and themember 1 to be measured is detached from the XY coarse movement stage 2.

According to this embodiment, it is possible to place the focus on eachof the probes 22 a to 22 c by adjusting the focus position incorrespondence with the position of the first scanner 10 by means of thesecond scanner 26. Further, the focus position can be adjusted threedimensionally, so that it is possible to prevent deviation in theoptical axis direction.

By monitoring the light amount of the light detection means 37 with thesecond scanner 26, it is possible to detect the optimum focus positions.A table of the optimum focus positions is prepared and used to controlthe position of the second screen 26 is correspondence with the positionof the first scanner 10. As a result, the focus position can be alwaysheld at the optimum position of each of the probes.

With respect to alignment adjustment during replacement of each probe,according to this embodiment, an operation or judgement by an operatoris not required for detection of the focus position and adjustment ofthe focus position, so that the alignment adjustment can be simplyperformed automatically.

Incidentally, referring again to FIG. 18, by effecting scanning with theprobe assembly in a direction of an indicated arrow A, it is possible tomeasure three points at the same time by the three probes 22 a to 22 c,so that a total measuring time can be reduced to ⅓ of that in the caseof using the single probe. Further, by measuring four or more points atthe same time, the total measuring time can be further reduced. When thescanning with the probe assembly is effected in a direction of anindicated arrow B, it is possible to obtain a result of simultaneouslymeasurement at three points on the same line. By applying a techniquewhich is called three-point method” to the measurement result, it ispossible to cancel motion error generated during the scanning. As aresult, measurement accuracy is further improved.

As described above, independently of the first scanner 10, it ispossible to successively place the focus on the three probes 22 a, 22 band 22 c by moving the focus of the “optical lever” optical system withthe second scanner 26. Further, from the output signals of the lightdetection means 37 and the position of the first scanner 10, bycalculating measurement values corresponding to the respective probes 22a, 22 b and 22 c, it is possible to perform simultaneous measurement atseveral points, i.e., multiprobing.

An effect of the multiprobing will be described more specifically.

As described above, when the scanning with the probe assembly iseffected in the direction of the arrow A, different three points aremeasured at the same time, so that the total measuring time is reducedto ⅓. Further, when the scanning with the probe assembly is effected inthe direction of the arrow B, it is possible to obtain the result ofsimultaneous measurement at three points on the same line. By applyingthe “three-point method” to the measurement result, motion errorgenerated during the scanning can be cancelled.

The three-point method will be briefly described.

When a position in a measuring direction is taken as x, three measuredvalues are taken as z₁ (x), z₂ (x) and z₃ (x), and a distance betweenadjacent probes is taken as δ, a difference formula g (x) representingsecond order differential is represented by the following formula (5):

$\begin{matrix}{{g(x)} = \frac{{z_{1}(x)} + {z_{3}(x)} - {2{z_{2}(x)}}}{\delta^{2}}} & (5)\end{matrix}$

The formula (5) shows that an influence of motion error of the probeassembly is cancelled. For example, when there is a vertical motionerror, the same offset is added to the three measured values z₁ (x), z₂(x) and z₃ (x) but the value g (x) is not affected based on the aboveformula (5).

When the above formula (5) is subjected to integration two times, it ispossible to obtain a shape. The thus calculated measurement resultcancels the motion error of the probe assembly.

According to this embodiment, in addition to the effect achieved byEmbodiment 1, the following problem can also been solved.

In the conventional technique, it has been difficult to be compatiblewith the multiprobing. However, in this embodiment, it is possible tomeasure each of bendings of the plurality of probes by moving the focusat high speed using the second scanner, so that it is possible to effectsimultaneous measurement at several points, i.e., multiprobing. Further,by the multiprobing, multipoint simultaneous measurement can beperformed, so that the total measuring time can be reduced. Further, byeffecting the multiprobing using the three-point method, the measurementaccuracy is further improved.

Incidentally, the timing signal 66 shown in FIG. 21 is selected so thatthe three probes are simply repeated. However, a similar effect can beobtained even when the order of selection of the three probes 22 a, 22 band 22 c is changed. For example, when the selection of the probes isrepeated in the order of 22 a, 22 b, 22 c and 22 b and 22 a, it ispossible to obtain a sampling frequency, of the central probe 22 b, twotimes larger than those of other probes 22 a and 22 c.

Embodiment 7

FIG. 11 illustrates an atomic force microscope according to Embodiment7. The atomic force microscope of this embodiment has the sameconstitution as that of the atomic force microscope of Embodiment 6except that an auto focus apparatus is incorporated in the opticalsystem of the apparatus of Embodiment 6.

The auto focus apparatus is fixed to the housing and includes a halfmirror 58, a lens 59, a cylindrical lens 61, and a four-piece photodiode62.

Light reflected by each of the probes 22 a to 22 c is diffusive lightsince focus thereof is placed on the reflection surface of the probe.The light is reflected by the beam splitter 34 and enters the halfmirror 58. The transmitted light enters the light detection means 37 andthe reflected light is converted into light converged by the lens 59 andpasses through the cylindrical lens 61 to enter the four-piecephotodiode 62.

The auto focus apparatus utilizing astigmatism described aboveintroduces therein light branched by the half mirror disposed in theoptical path of the light reflected by the reflection surface of theprobe. In addition to the light amount map, by using an output of theauto focus apparatus, a position of the probe is calculated. Also in theoptical axis direction, the light reflected by the probe diffuses, sothat the amount of light entering the light detection means isdecreased. For this reason, similarly as in the case of the directionperpendicular to the optical axis, an optimum position can be searchedwhile detecting the light amount. However, the NA of the “optical lever”optical system is small, so that the optical system is less sensitive todeviation in the optical axis direction, i.e., has a large depth offocus. Accordingly, the deviation in the optical axis directiondetectable by the light amount of the light detection means is low insensitivity.

In this embodiment, the light reflected by the probe is branched by thehalf mirror and deviation thereof in the optical axis direction isdetected by the auto focus apparatus. The auto focus apparatus has knownsome types but the auto focus apparatus utilizing the astigmatism hasbeen widely used as described above.

By using the auto focus apparatus, the measurement accuracy can beimproved even with respect to the deviation in the optical axisdirection, so that it is possible to cause the focus position toaccurately coincide with the probe position. As a result, themeasurement accuracy can be further improved. In addition, it is alsopossible to obtain the position conversion data in all the directionswith high accuracy by measuring the deviation in the optical axisdirection using the auto focus apparatus and measuring the deviation inthe direction perpendicular to the optical axis direction using thelight amount of the light detection means.

As described above, in the case where the measurement according to thenull-balance method in which the feedback control is effected withrespect to the Z fine movement axis so that the bending of the probe,i.e., the force acting between the probe and the member to be measuredis constant, the z fine movement axis and the probe are moved upward anddownward depending on projections and recesses of the surface of themember to be measured. By this upward and downward movement of theprobe, the focus position of the “optical lever” optical system is alsodeviated in the optical axis direction. However, in this embodiment, itis possible to obtain the position conversion data also in the opticalaxis direction with high accuracy, so that it is possible to correct thedeviation in the optical axis direction with high accuracy.Particularly, a roughened surface is subjected to measurement,displacement of the Z fine movement axis is large. For this reason, thetechnique of this embodiment is very important.

Embodiment 8

FIG. 35 illustrates an atomic force microscope according to Embodiment8. The atomic force microscope of this embodiment has the sameconstitution as that of the atomic force microscope according toEmbodiment 6 except that galvano-mirrors 71 and 72 are incorporatedtherein in an optical path of reflected light from each of the probes 22a to 22 c.

The galvano-mirror has been widely used as a light polarizing devicecapable of controlling an angle of a mirror at high speed by utilizingelectromagnetic force etc. It is also possible to control the directionof light in two directions by combining two galvano-mirrors each capableof controlling one angle of rotation. Further, by disposing a planargalvano-mirror using a torsion bar in the optical system, the focusposition can be moved at high speed.

In this embodiment, a light source 23 such as a semiconductor laser isprovided fixedly to the housing 6 so that emitted light is guided intothe optical fiber 24. The emission end 25 of the optical fiber, i.e., apoint source of light is fixed to the housing 6, so that converginglight ray is obtained by the lens 33 fixed also to the housing 6. Thetwo galvano-mirrors 71 and 72 are provided fixedly to the housing 6 andwhen the conversing light ray is reflected by the two galvano-mirrors 71and 72, it is possible to change the direction of this light ray.

The galvano-mirror is a device for controlling an angle of a mirrorreduced in size and weight utilizing electromagnetic force or the like,e.g., a device having such a structure that a mirror is fixed to arotational axis of a servomotor. By employing the small-size mirror anda high-output motor, it is possible to change the direction of the lightray at high speed.

By adjusting the angle of the galvano-mirrors, the direction of thelight ray is changed, so that the focus position can be changed.

In this embodiment, the galvano-mirrors are used, so that compared withEmbodiment 6, it is possible to effect higher speed scanning of thefocus position. Accordingly, it is possible to constitute an atomicforce microscope with shorter measuring time.

In this embodiment, the galvano-mirror including the mirror constitutedby the rotation-type servomotor is used but may also be constituted byusing a torsion lever prepared by processing a silicon wafer.

Further, in this embodiment, the mirrors are disposed between the lens33 and the polarization beam splitter 34 but may also be disposed at anyposition so long as they are located in the optical path. For example, asimilar function of changing the focus position is achieved by disposingthe mirrors between the prism 36 and the probe assembly.

As described above, according to the present invention, by providing thefocus position movement means for controlling the focus position of theoptical system depending on the probe position, it is possible to effecthigh-accuracy measurement in which the focus position of the opticalsystem is caused to follow the probe. Further, compared with the case ofintegrally moving the light source and the lens with the tube scanner,the end of the probe scanner can be reduced in size. Further, byadjusting the focus position of the optical system in the optical axisdirection depending on the probe position, measurement accuracy can befurther improved. In addition, the auto focus apparatus can meet measureof a member to be measured having an uneven shape with a relativelylarge unevenness (depth or height), of projections and recesses of theuneven shape, of several tens of microns or more.

In this embodiment, the displacement of the probe in Z direction isdetected by the optical detection means but the present invention is notlimited thereto. It is also possible to measure the displacement bydividing the incident light from the light source into two light rays,including one thereof caused to be reflected at the reflection surfaceof the probe and the other light ray caused to be reflected at areference surface, and by causing the two light rays to interfere witheach other.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purpose of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application No.038779/2006 filed Feb. 16, 2006, which is hereby incorporated byreference.

1.-10. (canceled)
 11. An atomic force microscope for measuring a surfaceshape of a member to be measured, comprising: a light source foremitting measuring light; a probe having a reflection surface; anoptical system for focusing the measuring light from said light sourceon the reflection surface of said probe; a housing for holding saidoptical system; a probe scanner, mounted to said housing, for holdingsaid probe and moving said probe in X direction, Y direction, or Zdirection relative to said housing; light detection means for detectingthe measuring light reflected by the reflection surface; processingmeans for processing displacement of said probe in Z direction on thebasis of an output of said light detection means; focus positionmovement means for moving a focus position of said optical system bymoving at least one optical element constituting said optical system ina direction including a direction perpendicular to an optical path ofthe measuring light; and control means for controlling drive of saidprobe scanner and said focus position movement means, wherein saidcontrol means drives said focus position movement means in synchronismwith drive of said probe scanner so that a focus position of themeasuring light focused by said optical system is on the reflectionsurface of said probe.
 12. An atomic force microscope for measuring asurface shape of a member to be measured, comprising: a light source foremitting measuring light; a probe assembly comprising a plurality ofprobes each having a reflection surface; an optical system for focusingthe measuring light from said light source on the reflection surface ofone of the plurality of probes; a housing for holding said opticalsystem; a probe scanner, mounted to said housing, for holding theplurality of probes and moving the plurality of probes in X direction, Ydirection, or Z direction relative to said housing; light detectionmeans for detecting the measuring light reflected by the reflectionsurface; processing means for processing displacement of said probe in Zdirection on the basis of an output of said light detection means; focusposition movement means for moving a focus position of said opticalsystem by moving at least one optical element constituting said opticalsystem in a direction including a direction perpendicular to an opticalpath of the measuring light; and control means for controlling drive ofsaid probe scanner and said focus position movement means, wherein saidcontrol means drives said focus position movement means in synchronismwith drive of said probe scanner so that a focus position of themeasuring light focused by said optical system is on the reflectionsurface of each of the plurality of probes by moving said focus positionmovement means between the plurality of probes.